Pigmented silicone elastomers



' tomers.

Patented Sept. 9, 1952 Theodore A, Te Grotenhuis, Olmsted Falls, Ohio Y No Drawing. Application December 7, 1946,

Serial No .'714,919

(o1. zen-27.5)

1, 18 Claims.

The present invention is a continuation-inpart of my application Serial No; 585,824, filed March 30, 1945, and relates to the preparation of silicone elastomers. It is particularly concerned with a process of reinforcing such silicone elastomers to provide increase in strength and other properties,

It is well-known that silicone elastomers or silicone rubbers with which thepresent invention is primarily concernedare able to withstand temperatures which are destructive to other elas- They heretofore have had exceptionally low tensile strength, which rarely, if ever, ex-

' ceeded 600 or 700 lbs/sq. in., even when compounded tvith the most desirable filling materials available. It has not been possible prior to my present invention to obtain reinforcement of silicone rubbers with carbon black, either because the carbon black has little aiiinity for the inorganic portion of the silicone or because the carbon black tends to absorb the curing agents necessary for curing of the silicone'elastomers, or because of both of these reasons.

It is an object of the present invention to provide a method of compounding silicone elastomers to obtain a high temperature-resistant material having improved properties.

It is another object of the present invention to provide a method of compounding organosilicone elastomeric material wherein pigments are utilized to obtain substantial reinforcement.

It is a further object of the present invention to provide a carbon black compound of silicone elastomers or silicone rubber having substantially improved properties over those heretofore produced and which can be cured or vulcanized.

It is still another object of the present invention to provide a pigment-reinforced silicone rubber which may be cured or vulcanized to the elastic state, giving tensile strengths in excess of 1,000 lbs/sq. in.

In my aforementioned, prior application, I described among other things the treatment of pigment with an organosilicon compound having a hydroxyl reactive group andthe preparation of rubbery and resinous material containing such pigments polymerized in place, etc. The present invention is primarily restricted to the silicone elastomers, etc., and their preparation.

In accordance with the present invention, the above and other objects, which will be apparent from the following description of the invention, may be accomplished by incorporating in the silicone polymer finely divided solid materials or Pigments having organic'groups connected through silicon atoms to the surface of the pigment. The organic groups may be connected to the pigment by separately treating the pigment with a'water-hydrolyzable or lhydroxy reactive organosilicon compound, i. e., a silicon compound capable of condensing or adding to hydroxyl groups, and the thus treated pigment thereafter mixed into the .silicone elastomer. Preferably, however, the pigment is incorporated into the elastomer before or during the preparation, condensation, or polymerization thereof. It may be -mixed into the monomeric 'materials used in forming the elastomer while they are in the liquid state, and retained therein during thelsubsequent polymerization or condensation reaction. The pigment, which may or may not have been previously exposed to a reactive organosilicon compound of a type capable of reacting withxa hydroxyl group, is thoroughly saturated or'has its surfaces thoroughly reacted during the reaction or subsequent polymerization or condensation to the rubbery state, so that it has littleyif any,

tendency to absorb curing agent and the like. In addition, it may have that intimate contact with the rubbery matrix only obtainable when the matrix has been fluid while in contact with the pigment 1 Ihe surfacesof most pigments, including even carbon black, surprisingly contain groups (apparently contain hydroxyl or carboxylgroups) which are capable of reacting with hydroxylreactive organosilicon compounds such as the hydrolyzable organosilicon halides, including the hydrolyzable alkylsilicon halides, the hydrolyzable arylsilicon halides, etc., the organosilicon amines, including the alkoxysilicon amines, etc., and to some extent even the organosilicates such as ethyl orthosilicate and the like, to form a chemical linkage to the surface of the pigment, as evidenced by the fact that pigments suitably treated with these materials are no longer readily 'wettableby water but will float thereon. The organosilicon groups attached'to the surface of the pigment, when provided with a plurality of hydrolizable groups or hydroxyl-reactive groups, maybe condensed withthe silicone monomeric materials or the silicone elastomers to form direct linkages to the pigment surfaces.

In the prepartion of rubbery silicone elastomers it is desirable to have'only monomeric materials that are capable of condensing bifunctionally, i. e., have only two groups that can combine with hydroxyl groups, so that the polymer will grow by condensation in only two directions and form long chains to give an elastic product. A com-- 12.00 as practicable, i. e., ordinarily between 1.98 and 2.00 andconsistin essentially-ofzdimethyl substituted silicon atoms, with a; suitable condensingagent such as ferric chloride hexahy- ,.,.d;r ate to convert ,the,:liquid.siliconeitoa slum;

. 4 which may later be vulcanized by a suitable vulcanizing agent such as benzoyl peroxide or other suitable strong oxidizing agent, etc.

The organosilicon dihalides, such as the dilinking with enhancement of resinous properties 5 methyldichlorosilane, are generally the preferred as distinguished from rubbery properties. When starting materials. These are hydrolyzed by the hydroxyl groups on the pigment surface are suitable hydrolyzing procedures to obtain a polyreacted with the silicone compounds containing merizable or condensable silicone oil which is only two hydroxyl reactive groups, direct attach condensed with a condensing agent, such as the ment can only be had to the pigment'particles aforementioned ferric chl'oridehexahydrate, to at the ends of polymer chains made up of the convert it to agum. condensed bifunctionally reactive silicones. When r Generally the hydrolysis of the diorganosilicon the hydroxyl group on the pigment surface is dihalides ..(preferably dimethyl dichlorosilane) reacted with compounds containing three or four should take place at relatively low temperatures, hydrolyzable groups, or groups condensable with 1'5 suchuaszerodegrees centigrade or below, as may hydroxyl groups, even if one ortw suchgroups be accomplished by mixing the silicon compound are utilized for reaction with the pigmenflsur-if 9 intoan ice and Water mixture with or without face, the attached silicone group may still enter solvent or diluent, such as butanol, ethyl ether, any part of bifunctionally growing chains.-- For and mixtures of one or more of these with benthis reason it is frequently desirable, even when zene, toluene, etc. The hydrolyzable organosili- :thepigment is incorporated into the liquid polycon dihalide may be diluted with solvent such as merizable materials which are to form the silicone anhydrous ether,, toluene, ,-etc., prior to the hyelastomers, to expose thepigment surface to the .drolysiswhich replaces, the two chlorines with direct action of compounds (preferably in vapor .hydroxyligroups. The silicon oil recoveredfrom phase) havingmore than two group capable of ...the hydrolysis iscondensed with any suitable-concondensing with hydroxyl groups. Thus, condensation catalyst, such as ferric chloridehexatact of the surface of the pigment with a silicon hydrate, for forming an elastomer. v1The condivtrichloride, preferably an alkyl trichlorosilane, or tions for the condensation, formingand curing of when the pigment is later to be incorporated into the rubbery. silicone elastomers are described in the silicone monomer, even silicon tetrachloride detail .in one or. moreof the aforementioned ,(tetrachlorosilane) is beneficial, particularly for patents and applications.

.,.the. finer, highly adsorptive pigments suchv as When the pigment is.treated,zprior to. its addi- ..carbon blacks, etc. .tion to .the monomeric materials utilized for The treatment of the surfaces of the pigment forming the. silicon elastomer, any organosilicon or the. condensation of the monomer in the compound havin an aminov g up, ahal se presence of the pigment, or both, tend to saturate group, or other groupcap'ableof condensing with e .the adsorptive capacities of the pigment so that .hydroxyl, may beutilized for treating: the pig- ,a curable rubber is obtained. ment. As. above stated, however,. the organo- The pigments which provide t greatest 1 silicon halides are preferred because of the ease .provement in properties of the-elastomeric mate- 40 w h W h th y react wit hydr yl groups to rials have relatively great surface areas and of all bond the silicon atom to the surface of .the pigi,pigments carbon black is preferred in that it gives ment through oxygen linkage.

-.excep'tiona1 properties to'the polymer when it is Because y havenorcarbon-to-carbon bond, ;.-incorporated thereinyin accordance with the =methyl=groups are the most desirable of the orpresent invention. Colloidal silica, such as that ganic groups in the :hydroxyl-reactive silicon prepared by burning ethyl silicate and collecting compounds. Such compounds having one or the residue by suitable electrostatic precipitation more organic groups selected from hydrocarbon meansis desirable. Examples of otherpigments or nonhydrocarbon groups, either aromatic, which may also. be present include zinc oxide, l p or l p i heterocyclicyeto, m y titanium dioxide, etc., coloring materials such as how ver, be use o iv stanti lbenefits in lead chromate,. antimony sulfide,.iron oxide and accordance-with the present invention. -Because .the like. Oneor more of these pigments may'also of e g eat e g h-of the carbon-to-silicon .be incorporated into the rubbery polymer, prefbond, in orderto Withstand relatively high temv,erably after treating it with a suitable reactive -peratures it is pr ferred that a carbon atom of silicone, to change the characteristics of the surthe-organic group be connected directly to the face thereof. Such pigments may be used in cona sil n a om. Organic compounds such, for exljunotion with the exceedingly finelydivided pigample, as diethoxy diamino silane, and other ments, such as the carbonblack, silica, or silicic l o i/amino (or halo) Sila es avi g a y or acid mentioned above. organic groups linked to silicon through an ,o, The silicone, elastomers of the type with which x n m, i a i to e ily y r lyzthe present invention is primarily concernedmay able groups, also are effective. Of all thesecombe prepared by, any suitable way, as, for example, binations the methyl silicon halides are preferred by any of the methods described in the copending as aforementioned, because of their reactivity and applicati n of Maynard c, A ens, s i l N because the methyl silicon is able to withstand 526,573, and thecopending application of. James much higher temperature than compounds hav- G. E. Wright and Curtis S... Oliver,: SerialNo. inga carbon-to-carbon bond. 526,472, both of which applications were fl1ed n Examples ofsuitable .organo-substituted: silicon March 14, 194%. halides which may .bev used for treating pigments Tney may be prepared by t ating a-djmethyl are: the. alkylesubstituted silicon chlorides such silicone havinga methyl to silicon ratio as near as d y y tpropylrbuty and lauryl silicon chlorides, etc. ythealkylenyl silicon halides such as -mono-,.di-. and trivinyl, allyl, butenyl and dodecyclenyl silicon halides,

. etc,. having .two ,totwenty carbon atoms-inat leastone.organicrgroup; the alkylenyl alkyl silicon chlorides such as allyl dimethyl silicon chloride, diallyl methyl silicon chloride, allyl methyl silicon dichloride, vinyl allyl methyl silicon choride, and allyl dimethyl silicon bromide, etc., having at least one halogen and at least one unsaturated group of two to twenty or more carbon atoms attached to silicon; the aryloxy or alkoxy silicon halides such as ethoxy silicon chloride and ethoxy diethyl silicon chloride; the alkoxy aliphatic-, alkyleneoxy aliphatic-, aryloxy aliphatic-, aryloxyaryland aliphatic-oxyaryl silicon halides such as butoxyethyl dimethyl silicon chloride, ethoxymethyl dimethyl silicon chloride, allyloxyethyl dimethyl silicon chloride, allyloxylauryl silicon trichloride, allyloxyphenyl dimethyl silicon chloride and phenoxyphenyl methyl silicon dichloride, etc. the halogen alkylenyl or haloalkyl silicon halides including chloroethylenyl dimethyl silicon chloride (chlorovinyl dimethyl silicon chloride), chloroethyl dimethyl silicon chloride and di(chloroallyl)methyl silicon chloride, etc.

In the treatment of pigments to react with organic silicon compounds such as aforementioned, it is preferred to suitably deagglomerate the pigment in the hydroxyl reactive silicon compound. The deagglomeration may take place during the preparation of the pigment, as by grinding or micro pulverizing the pigment in a relatively dry atmosphere of gaseous highly reactive organic compound such as a silicon halide as aforementioned, or by suitably ball milling or dispersing the pigment in an anhydrous liquid free from hydroxyl and comprising the reactive silicon compound. I

When as above pointed out the pigment with or without pretreating is incorporated into the hydroxyl reactive monomeric material such as the liquid dimethyl-silicon dihalide or when the pig:- ment treated as above described is incorporated into the oil produced by hydrolyzing this material, it is preferably dispersed therein by grinding with the monomeric material to produce a suitable dispersion. The grinding is preferably accomplished in a ball mill or by passing the rough mix of pigment and liquid condensable material through a colloid mill, so-called micropulverizer,'etc., which subjects the pigment to shear in the presence of the condensable or hydrolyzable and condensable polymer forming liquid material.

Dispersion of a pigment such as carbon black in the silicone oil is facilitated by thickeningthe oil as by incorporating therein a soluble or miscible polymeric silicone, such for example as the fluid (preferably viscus) or the soluble, solid polymeric aliphatic silicones, including the methyl and ethyl silicones, aryl silicones including the phenyl silicones and mixtures such as polymeric silicones. The dispersion is also facilitated by incorporating with the pigment monomeric material mixture (with or without the polymeric silicone) during grinding thereof a relatively small amount, such as about .1 to of the weight of the pigment, a suitable antiagglomerating agent. Antiagglomerating agents are particularly eiiective after the pigment or carbon black has been treated with organosilicon compounds reactive with hydroxyl groups.

In determining the relative suitability of antiagglomerating agents for the particular pigment to be dispersed in the silicone oil, the pigment (preferably treated as in Example 1 hereof with a hydroxyl-reactive organosilicon compound) is mixed with only suflicient monomeric material to form asurr puttylike paste. -The effectiveness of the antiagglomerating agent for the. particular pigment in the silicone oil is readily. apparent by applying a gram or two of this paste and a small amount of the proposed antiagglomerating agent on a glass plate and working it with a spatula. An efiective antiagglomerating agent will almost immediately cause a marked increase. in fluidity and an increase in jetness, showingimproved dispersion. A I i The antiagglomerating agents soluble in silicone'oils have more dispersing effect, and of these materials the cationic agents appear to be most efficient. Examples of these antiagglomerating agents that are particularly desirable are the soluble phosphatides and substituted amides of alkyl phosphates having ten to twenty carbon atoms, such as the substituted amide of alkyl phosphate (twelve carbons) and the substituted amide of alkyl phosphate (eighteen carbons), sold respectively under the trade name Cationic Agent C and Cationic Agent D by Victor Chemical Works.

Example 1 grams of unbeaded carbon black are subjected to agitation in the presence of a vapor from about one gram of a mixture of mono-, diand trimethyl silicon chlorides obtainable under the trade-name Dryfilm from The General Electric Company. The agitation is continued in'the presence of the alkyl silicon halide for about'ten minutes to allow thorough penetration of the vapor. The hydrochloric acid formed by the reaction may be removed in any suitable manner, as'for example by heating at elevated temperature, by neutralizing with an alkaline material such as dry NH3, by shaking the carbon black with water (washing), or'preferably by treating the carbon black with ether and water and washing the carbon black-ether mix until free from acid. The carbon black thus treated has much less tendency to be wet by water and much greater tendency to be wet by hydrocarbon organic solvents.

Example 2 When titanium dioxide is substituted for carbon black in Example 1, and agitation continued in like manner, it is also more readily dispersed in organic liquids.

Example 3 Into 300 parts by weight of a liquid consisting essentially of dimethyl silicon dichloride, but containing a small percentage of methtyl silicon trichloride and about 5 or 10 parts of a soluble polymeric silicone to act as a thickening agent, is incorporated about 20 to 25 parts of carbon black. Moisture or OH groups on the carbon black immediately reacts with a portion of the silicon halide with apparent bonding of organosilicon groups to the surface of the carbon blackparticles. Thisis evidenced by the fact that they become unwettable by. water on contact with organosilicon halide liquid or vapor.

The slurry thus had may be ground in a ball mill under substantially anhydrous conditions to at least partially disperse the carbon black. The remaining silicon halide of the mixture is then converted into organic silicon hydroxy compounds, as by treatment with cracked ice. By shaking the mixture with an organic solvent for the silicon compounds such as ether, the hydroxy organosilicones (organosilicols) as well as most of the treated carbon. black are readily, separated 'iromitheiaqueousmaterial; Thisisadueltotheriact that: the: carbon black-is "more readily wetted by the etherzthan' by the water andiduei tothesolubility of; theisilicon hydroxy compound'in'ithe ether. After washing the'ether free'of acidpitis concentrated: by" vaporization at slightly elevated temperatures. A viscousliquid-suitable'for. adhesives and surface coatings. is. obtained; a By further heating at elevated temperatures; preferably in the presence of 1 to 5% of an alkyl'borate, such as triethylborate, resinous-bodies of the'ldesired flexibility andahardness-may be obtained, whichbodiescontain the carbon black therein.

Example 4- C'arbon black treated .as in'Examplel with a mixture. of mono-, diandtrimethylsilicon chlorides is agitated; with-cold water to remove the hydrochloric acidformed by reaction. vIt is then stirred into the washed ether solution of a ,hy drolysis product obtained byhydroliaing-av mixtureof dimethyl silicon. dichloride and methyl silicon trichlo-ride with cracked ice as in the preceding example. The amount of carbon black used is about or- 14%;"or even considerably moreof the weight .oftheoriginal alkyl silicon halide. After concentratingthe ethersolution containing carbon. black, the ingredients are-in;- corporated in aclosed ball mill and ground with heating, up to .or- C. to faciliate-dispersion of the carbon black and; simultaneous condensation of the-methyl silicon hydroxides toa silicone polymer of the desired consistency;

' Efcample 5 Thirty parts of carbon .blaclg treatedi'as in Examplel with a mixture of mono-', di-and'trimethyl silicon-chlorides: is agitated With cold water. toreinove the hydrochloric acid formed by thereaction. The. product is then stirredv into 100 parts'of silicon oil obtained: by .hydrolyaing a substantially pure dimethyl silicon dichloride atlowltemperature. a I

. The mixture-thus obtained is .ground in a ball mill for a few hours to' produce a-fiipghsipnof the carbon black in the silicon oil. The dispersion is improved and-rendered more fluid by the addition of -a-.relatively small amount; say about 5% (basedon-the weight of -.the'-polyfmerizab1e or .condensable'silicone oil) of. a soluble oily'silicone polymer of diethylsilicone and-about 1%; of

' state. with a :suitable condensing agent, such as ferric-chloride;hexahydrate. i The polymertthus obtained after mixing with a-vulcanizingagentpr oxidizing agent, such as aboutffourzparts-iof an organic peroxide and curing-for several hours at elevated temperatures of about C., as men tioned in the i aforementioned applications, :has exceptional high strength compared. to'-' silicone rubberswhich do not contairiithe icarbon black", indicating" much reinforcementr'by:the carbon black.

.The .carboniblack used in the above Example 5 may be substituted by treated :or untreated car .bon black and'may befstirredi-or dispersed directly into the" dimethyl' silicon dichloride iandfthe err- -tire mixture-subjected to. the 'hydrolyzing'rtre'atmentto produce thersiliconeoil which ma be polymerizeden mass'e'inthe presence of a suitable condensing'iagent', such asferric chloride :hexahy drate; etc;- as set forth fin one or moretcofthe aforesaidapplications, to fc'rmthe' rubbery "polymar whl'chllls'ithefi'COmDOllIldBd with al curing .agent,such:'as a tblllGIlBiiSOllltlOIlOf about 3% bEifSBdOH 'thenpolymer of benzoyl peroxide, and cured" at elevated temperature to-produce. a reinforced rubber of high tensile strength. When, on the other hand, untreated carbon. black is simply milled into the silicon elastomer, the curing usuallyis substantially prevented for some reason, .pr'obably-becauseof absorption of curing'agents.

If desired, the reinforcing pigment, such as carbon black; may be wetteol'with a hydroxyhreactive-silicon compound, preferably a diorgan- .osilane suchas the dimethyldiohlorosilane, or. a solution in nonreactive solvent .such as toluene, 913C;Of'JhYdI'OXYIE-EBaCtlVG organo silane, or asa halosilane; or'dimethyl dichlorosilane, and .then the wet mixture masticated' into amass or" silicone rubber, which may .or may not be vulcanized. The: carbon black. is preferably Wetted with the 'hydroxyl-reactive silicon compound a substantial time'beforethe mix. is incorporated into the polymer to insure complete saturation of adsorptive-tendencies of-the carbon black. Unreacted hydroxyl-reactive groups of the dimethyl dichlorosilane, etc., in the carbon black: mixture, function both to reclaim and reinforce the vulcanized silicone. The following examples illustrate this feature: 2

Example 6' Sixty gramsiof unpelletized channel black (W6) are mixed with 100 grams of a 15% solution of di'methyl dichlorosilane in. anhydrous toluene. The wet mixture is allowed to stan'dfor at least one hour and then slowly milled intolflll grams of a rubbery silicone elastomer prepared in the ordinary way'by condensing a dirn ethyl silicone oil having amethyl-to-silicon ratio of approximately two in the presence of .ferric chloride hexahydrate until a gumlike mass'is'obtained. During the initial mixing of the wet mixture into the rubbery polymer the mix is maintained at about'room temperature (or preferably below) by cold water in the mill rolls. The milling 'is continued very slowly on a tight millat elevated tern perature'until a major portion of the solvent and volatile matteris dissipated. About 3 ofbenzo'yl peroxide is then added and the millingcontinued for'around five minutes. The product is molded and cured for'several hours and exhibits strength and'elasticity much higher than articles cured from silicone rubber without the carbon black addition. I

' If'd'esired; the hydrochloric acid may bewashed out of thefsilicone polymer after the wet carbon black addition by addition of water with the polymer on washing! rolls. The product is then dried, furthercompounded with the vulcanizingagent, and then cured.

Example 7 When in" the above Example Bthe silicone rub her is a cured silicone elastomer, it is masticated on mixing rolls until torn apart and then mixed with. the carbon black dimethyldichlorosilane toluene'mixture'prepared as above and preferably having an excess of dimethyldichlorosilane over and above that which reacts With'the' "carbon black. Theresultant'product after curing also has exceptionally desirable properties.

. While methyl halosilanesare preferred for treating carbon black, etc., other hydroxyl reactive siliconcompounds may be used as aforemen tion-ed: Compounds containing no carbon-towaricarbon'bondsz-are usually required when theco'mpoundsare itd stand the highesttemperatures.

,9, Any solvent for the polymer that is free from groups reactive with thesilicon and polymer may be used in place of the toluene in the above Examples 6 and '7. In the above examples the curing agents are not absorbed by the carbon black and a relatively highly reinforced polymer is produced. The dry treated carbon black of Example 1, with or without washing, may be incorporated intothe silicon elastomer direct and, while the strength of the rubber produced is not as great as that in the preceding examples, it is much improved over those of siliconrubbers which are not compounded with carbon black, and is much superior to silicon rubbers compounded with untreated carbon black and hence not curable by known means. In place of the carbon black, other pi ments, as aforementioned, especially those having a surface area in excess of 30 square meters per gram, may be used to obtain desirable results.

The amount of pigment used depends, as is well-known by rubber compounders, on the particular pigment, the hardness and the tensile strength desired in the vulcanized product. The amounts used are therefore variable over wide limits. In the case of very fine pigments, such as black or white carbon blacks, which have a surface area of 25 or more square meters per gram, at least 15, parts per 100 parts of the elastomer are usually required for much reinforcing efiect and about 25 or 30 parts to about 60 or '70 parts are usually preferred. More than 100 parts per 100 parts of elastomer may be objectionable in many instances. In the case of pigments having larger particle size, such as pigments having a surface area of less than 20 square meters per gram, as much as 200 or even 300 parts may be used and a very small amount may be found to give desirable efiects.

It is pointed out above that the pigments are treated to modify their surface characteristics by contact with a fluid-reactive silicon compound, such as the amino and halosilaneawhich have a group capable ofreacting or condensing with hydroxyl groups to split out hydrochloric acid, ammonia, water, etc. It is preferred that these silicon compounds have an organic group attached to the silicon atom, but, as aforementioned, substantial efiect can be obtained, particularly with a process similar to that disclosed in Example 7 above, when the amount of silane is substantially limited to that which can react with the surfaces of the carbon black or pigment, with a hydroxyl-reactive silicon compound, such as silicon tetrachloride, which does not contain organic groups. Excess of such material is undesirable because of its marked cross linking nature.

The treatment of carbon black with the more reactive silicon compounds, such as those containing amine or halogen groups linked directly to silicon, produces a more rapid modification of the carbon black and saturation of its absorptive tendencies by mere contact with the carbon black, but a prolonged period of contact between the carbon black and the less reactive fluid organosilicon hydroxides, as occurs during polymerization of those materials to the rubbery state, also has a very substantial tendency to saturate the absorptive tendencies of the black so that a cured rubbery silicone article may be had.

Pigments having vinyl groups attached to their surfaces through silicon are claimed in my copending application, Serial No. 251,152, filed October 12, 1951.

It is also apparent that modifications of the invention maybe made without changing the spirit thereof, and it is intended that the invention be limited only by the appended claims.

What we claim is:

1. A carbon black-reinforced dimethylsilicone elastomer containing carbon black, surface portions of which are modified bythe residue from the hydrolysis of a hydrolyzable organo-silane.

2. In a method of compounding a vulcanizable diorganosilicone elastomer, the steps which comprise treating a. carbon black to modify its surface characteristics with a fluid comprising a silicon compound containing attached directly to silicon a water-hydrolyzable group, said silicon compound being selected from the group consisting of silicon tetrahalides andorgano-silicon compoundsand mixing the thus treated carbon black with said vulcanizable silicone elastomer, whereby theabsorptive capacity of said carbon black to, curing agents in said elastomer is reduced.

3. In a method of compounding a rubbery diorganosilicone elastomer, the steps which comprise mixing carbon black with a hydrolyzable o'rgano halosilane-containing composition, and

thereafter mixing the thus treated carbon black into said vulcanizable silicon elastomer.

4. In a method of compounding an elastomeric condensation product of a hydrolyzed hydrolyzable organosilicon compound containing only ,two hydrolyzable groups attached directly to a silicon atom, the steps which comprise mixing a carbon black with a solution of a hydrolyzable methylhalosilane, and thereafter mixing the carbon black-solution mix into said condensation product. I

5. A dimethylsilicone elastomer comprising a polymerized dimethylsilicone oil having a methyl-to-silicone ratio of about two and com prising a carbon black modified by contact with a hydrolyzable fluid organo halosilane..

6. A method of treating a vulcanized dimethylsilicone elastomer which comprises mixing with said elastomer a mixture of carbon blackand a hydrolyzable organic halosilane.

7. In a method. of preparing a reinforced dimethylsilicone elastomer wherein a pigment having a surface area in excess of 20 square meters per gram is incorporated in said elastomer, the step which comprises subjecting said pigment to a fluid dimethylsilicon compound prior to incorporating it into contact with said elastomer, said silicon compound having attached directly to a silicon atom in addition to methyl groups an inorganic group which is free of carbon that condenses with hydroxyl groups, whereby the adsorptive capacity of said pigment for said curing agent is reduced, said silicon compound being one which reacts with hydroxyl groups through said inorganic carbon free group to form a product having a 51-0 bond.

8. The method of claim 7 wherein the fluid silicon compound is a hydrolyzable halosilane.

9. In a method of preparing a carbon blackreinforced dimethylsilicone elastomer, wherein a curable dimethylsilicone elastomer is mixed with carbon black and the mixture cured and vulcanized, the steps Which comprise deagglomerating said carbon black in the presence of an organosilicon compound containing attached directly to a silicon atom thereof besides an organic group an inorganic group which is free of carbon and which reacts with hydroxyl groups, and incorporating the thus treated black into said elastomer, said organosilicon compound being one which 1 1 reacts with- =hydroxyl groups through said fhydroxyl' reactive groupto: form; a Si-Obond.

The rnethodof claims-wherein the-dea glomeration is accomplishedrby grindingthacanbon black in the presence of a fluidcornprising a hydrolyzable Ineth'ylsiliconhalide.

'11. A composition comprisinga ulcanizable rubbery dimethylsiliconeelastomer and distributed through said elastemer a pigmenthaving a surface area ofever-ZO squarem'eters per-gram, which pigment has on surface portions thereof a residue from the treatment of said pigment with an organosilicon compound containing attached to silicon one inorganichydroxyl-reactive group which is free .of carbonand-one organic groupnot reactive to water, whereby thesuriace characteristics are modified and--- tendency for adsorption-of curing agents ismaterially reduced, said-oiganosilicon compound being one which reacts with hydroxyl groups through: saidhydroxyl reactive group to i form a Si Obond;

WIZVQA composition" accordingto claim 11 wherein. said pigment is a a finely dividedsilica haying a surface "area of-over- 30 square meters perigram and-said pigmentis dispersedthrough said elastomer. i

13. Th'gcomposition or claim 1-1: wherein said rubbery condensation product consists essentially of-dimethyl siliconoxideunit and said pigment is a finelydividedsilica having a surfacearea-of more than 39 squar meters per gram, and whereinthe organo silicon compound i hastwo hydroxyl reactiye groups and-is free of carbonto -car-bon bonds.

14; J The composition of claim 11 wherein said rubbery condensation product consists essentially of dimethyl silicon oxide units,- andsaid pigment is a finely divided silica hay-ing a surfac -area of more thanBOgsquare meters per" gram, and wherein the organoE-silicon compound has two hydroxyl reactive groups,

'15.. The product of claim 11 wherein said hydroxyl reactive-groups which are split off with' H from fcontacting '-OH to form a -new-silico noxygen bond are Nile-groups; and wherein said pigment is an inorganic pigment-- which is substantially free of elementalcarbonv andwhich has asurfacearea of overl3il square metersper gram. V

16. A composition comprising .a vulcanizable di-organosilicon elastomer having dispersed therethrougha finely divided silica which has on surface portions thereof a-residue from the treatment oi said pigment with a silicon compound containingatta'ched directly to silicon a waterhydrolyzable group, said silicon compound being selected from the group consisting of-=si1ic0n tetrachloride and organo-silicon compounds.

17; A composition according to claim 11 wherein said pigment-is a finely divided silica and organic 'group attached to silicon is an alhylgroupL 18 A composition according to claim 11 whereinsaid pigment is a finely divided silica haying asurlfacearea over 30 square meters per gram andw herein said residue on the pigment u c m rise a ens-sno- Qrmlpv THEQDOPJE A. TE- GROTENHUIS:

REFERENCES: CITED,

The following references are of'record in the file of thispatent:

U I ED; STATES PATENTS Number Name Date 2,306,222 Patnode June ,22, 1942 2,424,853 Safford July 29, 1947 2,448,756 Agens- Sept. 7, 1948 2,452,416 Wright Oct. 26,1948 2,460,7951 Warrick. Feb. 1, 1949 2,486,674 Pedersen Nov. 1, 1949 2,510,661- Safford June 6; 1950 OTHER, REFERENCES" Silicone. Rubber, a General Electric Development,{-Rubb,er Age;- vol. 56,;No, 2, November 194-4, page, 174,- 

16. A COMPOSITION COMPRISING A VULCANIZABLE DI-ORGANOSILICON ELASTOMER HAVING DIPERSED THERETHROUGH A FINELY DIVIDED SILICA WHICH HAS ON SURFACE PORTIONS THEREOF A RESIDUE FROM THE TREATMENT OF SAID PIGMENT WITH A SILICON COMPOUND CONTAINING ATTACHED DIRECTLY TO SILICON A WATERHYDROLYZABLE GROUP, SAID SILICON COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF SILICON TETRACHLORIDE AND ORGANO-SILICON COMPOUNDS. 